How to manage large amounts of image data for training?
I suggest you fine-tune an existing model. Knowledge transfer models in many image processing tasks are now open sourced and you can build your model on top of them. Also, knowledge transfer models are trained on a large datasets and can quickly converge to your case-study with a little of task-specific extra training. 


  This way you will use few data to tune the model which leads to less
  memory use and less training time. You will also take advantage from a
  ready-to-use architecture and get accurate results.


Depending on your case-study you can choose from this list of computer vision pre-trained models.